Remove Debian 9 from the puppetdb pipelines defined in jenkii/enterprise/projects/puppetdb.yaml in ci-job-configs.
Verified 6.x, 7.x and main streams passed without debian 9:
https://jenkins-enterprise.delivery.puppetlabs.net/view/puppetdb/view/6.x/job/enterprise_puppetdb_integration-system-puppetdb_full-6.x/1426/ https://jenkins-enterprise.delivery.puppetlabs.net/view/puppetdb/view/7.x/job/enterprise_puppetdb_integration-system-puppetdb_full-7.x/33/ https://jenkins-enterprise.delivery.puppetlabs.net/view/puppetdb/view/main/job/enterprise_puppetdb_integration-system-puppetdb_full-main/1082/